In the context of this specification, a streamer ball is a ball for use in tennis-type ball games of a type having an impact body and a tail comprising a number of elongate flexible streamers which are attached to the impact body for stabilizing the flight orientation of the ball. Streamer balls of this type are known.
A streamer ball of this type is disclosed in U.S. Pat. No. 5,813,931 (assigned to European Sports Merchandising BV). The streamer ball comprises a ball and a tail comprising a number of elongate streamers directly attached to the ball and extending therefrom, for use in tennis-type bouncing ball games. U.S. Pat. No. 5,813,931 discloses a number of performance parameters for such a streamer ball and specifically for the tail of the ball, that provide for desired bounce and flight qualities that enable a tennis-type game to be played with such a streamer ball. The use of a tail connected to a ball has a number of benefits when playing a tennis-type ball game. Firstly, the use of a tail which trails behind the ball in flight creates drag which slows the ball down so that when the ball is struck with a bat, the distance that the ball can travel is effectively reduced, thereby permitting a tennis-type ball game to be played in a relatively small area while the ball can still be struck at “full strength”.
A further benefit of such a tail is to reduce any tendency of the ball to spin or swerve during flight. The tail streams out behind the ball in flight so as to define a dynamically changing and fluttering asymmetrical profile which rapidly reduces any side spin or top spin or swerve which is imparted to the ball upon impact by a bat, thereby causing the ball to follow a regular flight path.
A disadvantage associated with the use of a ball having a tail formed of a plurality of streamers which are directly attached to the ball as is disclosed in U.S. Pat. No. 5,813,931, is that the tail, during play, becomes tangled with the bat or the ball, resulting in interference with the flight of the streamer ball and the streamers being destroyed relatively quickly. This disadvantage is overcome by the streamer ball disclosed in PCT/IB02/04673 (Gormley). The streamer ball includes a tail having an elongate flexible spacer stem and a number of streamers that are spaced from the impact body by means of an elongate spacer stem. The spacer stem defines an anchor formation at one of its ends, whereby the stem is anchored to the impact body and an attachment formation at its other end, whereby the streamers are attached to the stem. With the tail separated from the ball by the spacer stem, the streamers cannot easily become tangled with the bat or the ball.
A further benefit of a spacer stem is that in spacing the streamers from the streamer ball, the effect of the streamers on the regulation of the flight path of the ball, is enhanced. The extra leverage afforded by the streamers pulling on the distal end of the spacer stem rather than directly on the impact body dramatically improves the flight stability of the streamer ball. As such, after impact with a bat or playing surface the provision of a spacer stem enhances the ability of the streamer ball to rapidly regain an aerodynamically stable attitude in flight.
An important performance characteristic for a ball which is intended for use in tennis-type bat and ball games, is that the ball should have sufficient bounce after striking a playing surface to enable the ball to be struck by a player after bouncing. An effect of the attachment of a flexible tail to a ball is that the mass of the tail causes a reduction in amount of bounce of the ball. A flexible tail deforms when the ball to which the tail is attached, impacts a bat or playing surface and consequently acts as a shock absorber dissipating some of the energy which is transferred to the ball upon impact, thereby reducing the spring of the ball off the bat or playing surface. It is thus particularly important in the case of a streamer ball which is intended for use in tennis-type bat and ball games, to provide a flexible tail assembly wherein the free part of the tail assembly disposed externally of the ball, is of negligible mass compared to the mass of the ball to which the tail assembly is attached, so as to have a minimal effect on the bounce height of the ball.
Strung racquets are usually provided with a network of strings under tension strung across a frame at the head of the racquet. When using a strung racquet, the resilient compressibility of the ball-striking surface of such a racquet, provides a “trampoline effect” which allows the ball to dwell on the ball-striking surface at impact for a significantly longer period of time than is the case with a bat which has an untensioned ball-striking surface. Due to the inherent resilient compressibility of the ball-striking surface of a strung racquet, the balls selected for use therewith can allow for less compression upon impact compared to a ball which is designed to be struck by a bat. An important consideration in the design of a ball for use in bat and ball-type games played with a bat having an untensioned, rigid ball-striking surface, is that the ball should have sufficient resilient compressibility so that when it is struck by the bat or the ball bounces on a rigid playing surface, the dwell time of the ball upon the bat or playing surface at impact is sufficiently long as indicated by the relative depth of compression of the ball, so as to transfer adequate kinetic energy to the ball so as to provide the necessary spring off the bat or playing surface and consequently a satisfactory impact feel, sound and impact speed when leaving the bat or playing surface after impact. The greater the compression of the ball upon impact, the greater the amount of energy which is stored in the ball which in turn causes greater spring off the bat or playing surface when the energy is released as the ball regains its shape after the initial impact. There is thus a direct relationship between the depth of compression and the amount of energy which is stored by the ball upon impact and released immediately after full compression is achieved. It is for this reason that the current Applicant has sought to design streamer balls wherein the balls have a high degree of resilient compressibility in order to achieve a high degree of spring off a bat or playing surface.
A further important consideration in the design of balls for use in tennis-type bat and ball games played with bats having untensioned, rigid ball-striking surfaces, is that the balls should have sufficient mass in order for the ball to compress sufficiently upon impact in order to provide the trampoline effect referred to above, off a bat or playing surface and also to achieve solid contact between the ball and the ball-striking surface of a bat.
The current Applicant has identified a need to supply bats having rigid, untensioned ball-striking surfaces having a relatively low weight. The cost of the bats in sets of bats and balls is the major component of such sets. It is an object of the present invention, to provide for the production of relatively lightweight bats which use less material and are thus relatively inexpensive to produce. It is also a requirement for bats which are to be used by children, that the bats must be relatively lightweight. In order to do so, it is necessary to provide balls for such bats which are correspondingly light in weight and which are matched in terms of their weight to the weight of the particular bat with which the balls are to be used. In this regard, the Applicant believes that a bat should be at least five times heavier than a ball to be used therewith and preferably, at least ten times heavier than the ball so as to provide a solid impact feel and avoid unpleasant jarring and vibration upon impact. As a result of the provision of relatively lightweight bats is that the balls used with such bats must also be correspondingly light in weight. The current Applicant has encountered a problem with streamer balls having relatively lightweight impact bodies having a mass of less than 30 g (excluding the mass of the streamers) which allow for the use of relatively lightweight bats. Such streamer balls having relatively lightweight impact bodies are unable to achieve the compressibility required for adequate impact performance, due to their lack of mass in relation to the compressibility of the frontal impact zone of such impact bodies. It will be appreciated that the streamers, due to their high degree of flexibility and low mass, are unable to exert a material force on the frontal impact zone of the impact body upon impact.
The abovementioned characteristics of streamer balls can be contrasted with a shuttlecock, for example, for use in badminton games wherein the shuttlecock is not allowed to bounce in terms of the rules of badminton. The base of a shuttlecock is typically of cork or plastic having an outer fabric or leather cover, which has negligible resilient compressibility and a skirt which is attached to a rear end of the base. The skirt typically comprises a cone-shaped circle of feathers or a similarly shaped integral injection moulded plastic structure. There are a number of differences between shuttlecocks and streamer balls as described hereinabove. Firstly, the configuration of the skirt of a shuttlecock is that of a semi-rigid, symmetrical conical structure permitting a degree of spin in flight by slicing or striking the base at an angle, at low speeds, to the face of the racquet. A large degree of the flight stability of a badminton shuttlecock is derived from the gyroscopically acting centrifugal forces imparted by the axial spin of the shuttlecock in flight, derived from the angled fluted surface of the skirt. At low speeds this stabilizing effect is greatly reduced and the shuttlecock is much less stable in flight. For this reason, overhead service similar to that in tennis, is impractical as the shuttlecock is unstable at the low speeds of the shuttlecock when it is tossed up by hand prior to the service stroke. As stated above, the streamers of a streamer ball have a dynamic fluttering asymmetrical profile in flight as exhibited by the independent movement of the individual streamers making up the tail assembly and are thus designed to reduce spin. Under normal flight conditions, a streamer ball has no axial spin. Secondly, as badminton games are played with tensioned racquets, the base of the shuttlecock has negligible resilient compressibility as the inherent resilience and compressibility of the racquet face provides the required trampoline effect upon impact with the base of the shuttlecock. As such, a shuttlecock is entirely unsuitable for playing a game wherein the shuttlecock is struck by a bat having an untensioned, rigid ball-striking surface. Thirdly, the portion of the skirt of a shuttlecock which projects from the base, typically has a high mass relative to the total mass of the shuttlecock (typically approximately 30% of the total mass of the shuttlecock) which permits a tumbling net shot to be played wherein the shuttlecock is sliced at low speeds causing it to tumble over a few times. As bounce is not allowed in badminton games, the relatively high mass of the skirt is not disadvantageous but desirable so as to produce the required flight characteristics for badminton games. Streamer balls are far more stable at low speeds. Fourthly, as the skirt of the shuttlecock is directly attached to and extends directly outwardly from the base, this presents similar problems to those encountered with streamer balls wherein the streamers are directly attached to the ball, namely, that if the shuttlecock is struck at an angle to its flight path by a bat, the skirt is often struck causing damage to the skirt. In addition, the skirt protrudes outwardly from the base at a far greater angle than the spacer stem and tails of a streamer ball which exacerbates the problem. Fifthly, because the mass of the skirt is relatively high compared to the mass of the base and consequently as the centre of the mass of the shuttlecock is spaced a significant distance rearwardly of the centre of mass of the base (without the skirt), the shuttlecock takes a relatively long time to turn over after impact by a bat and regain an aerodynamically stable attitude in flight, thereby rendering the shuttlecock unsuitable for playing games at low speeds in relatively small playing areas.
U.S. Pat. No. 4,538,818 discloses a “shuttlecock” which can be used with a variety of bats or racquets for both badminton and tennis-type games. The base (referred to as a “head”) has a spherical shape of tennis ball size and is designed to bounce. Although the shuttlecock disclosed in U.S. Pat. No. 4,538,818 is designed to bounce it still suffers from the same deficiencies as described hereinabove in relation to a conventional shuttlecock. In addition, as the mass of the skirt is relatively high compared to the mass of the base, causing the centre of mass of the shuttlecock to be spaced a significant distance rearwardly of the centre of mass of the base (without the skirt), the shuttlecock takes a relatively long time to turn over in flight and also to regain an aerodynamically stable attitude in flight, thereby rendering the shuttlecock unsuitable for playing games in relatively small playing areas. Furthermore, the offset between the centre of mass of the shuttlecock and the centre of mass of the base (without the skirt) causes erratic bounce off a playing surface due to the centre of mass of the shuttlecock being spaced a significant distance rearwardly of the impact zone of the base. The shuttlecock design disclosed in U.S. Pat. No. 4,538,818 cannot be applied to shuttlecocks having relatively small bases (of a size smaller than that of a tennis ball) as either the lack of mass in the smaller base will render it unstable in flight and unable to compress sufficiently at impact or if the density of the base is increased it renders the base less resilient and unable to achieve the compressibility required for adequate impact performance. It is for this reason that the shuttlecock disclosed in U.S. Pat. No. 4,538,818 is described as a “large” shuttlecock having a head of a size comparable to that of a tennis ball.
Reference is made herein to a “drop test”. In this test which is commonly used for balls of various types, the streamer ball is dropped (with a spacer stem attached to the impact body but without any streamers attached to the spacer stem) with its impact body facing downwards with the spacer stem in a vertical orientation, from a height of 254 cm (100 inches) onto an untensioned, rigid, flat, horizontal, solid impact surface such as concrete or a thick steel plate, and the resulting compression of the impact body of the streamer ball upon impact with the impact surface and/or the height to which the ball bounces after impacting the surface, is measured. In order to determine the bounce height of a ball, the maximum height to which the ball bounces after impacting the impact surface is measured. For example, the International Tennis Federation specification for the bounce height of a tennis ball is between 135 cm and 147 cm when subjected to a drop test from the same height. A number of techniques are used to measure the compression depth of a ball upon impact with the impact surface. One such technique involves marking the impact zone of the ball with a transferrable marking substance, such as talcum powder, measuring the dimensions of the mark left behind on the impact surface after impact by the ball and applying the dimensions of the mark to the geometry of the ball, calculating the depth of compression of the ball upon impact. Any reference hereinafter to a “drop test” must be interpreted to mean the test described hereinabove wherein a streamer ball is dropped (with a spacer stem attached to the impact body but without any streamers attached to the spacer stem) from a height of 254 cm onto a rigid, flat, horizontal, solid impact surface.
It is an object of the present invention to provide streamer balls having relatively low mass impact bodies having relatively soft, low density frontal impact zones so as to achieve a high degree of compression upon impact by a bat or playing surface, but which have particular design features which take into account the abovementioned design criteria and deficiencies and which render the streamer balls particularly suitable for use in tennis-type bat and ball games played with a bat having an untensioned, rigid ball-striking surface.